08-03-23 - U and Es Flashcards
Learning outcomes
- Awareness of the theory of fluid and electrolyte balance.
- Understanding of the concepts of volumes, compartments, content, concentration and input/output.
- Appreciation that fluid and electrolyte balance is central to the provision of appropriate acute clinical care
What substances are measured when looking at fluid and electrolytes in Fife?
What 2 other values can be calculated?
What do U and E measurements allow clinicians to do?
- Substances are measured when looking at fluid and electrolytes in Fife:
1) Na, K, Creatinine
* Fitted as standard
2) + Urea
* For hospital patients on request by GP’s
3) Cl-
* Available freely on request
4) Bicarbonate
* Available on request hospital patients, too unstable for out-patient requesting
- 2 other values can be calculated:
1) eGFR
2) AKI flags. - U and E measurements allow clinician to make a broad estimate of water status.
What are 3 relates systems/hormones to Us and Es?
- 3 related systems/hormones to Us and Es:
1) Anti-diuretic hormone
2) Renin-angiotensin system
3) Aldosterone
What are 3 cases in which abnormal electrolytes can be present?
What 4 processes are electrolytes important for?
- 3 cases in which abnormal electrolytes can be present:
1) Primary disease state
2) Secondary consequence of a multitude of diseases
5) Iatrogenic problems are very common
* Relating to illness caused by medical examination or treatment.
- 4 processes electrolytes are important for:
1) Maintenance of cellular homeostasis
2) Cardiovascular physiology - BP
3) Renal physiology - GFR
4) Electrophysiology - heart, CNS
What are the normal ECF and ICF concentrations/volumes for water Na+ and K+ (in picture)?
What are 6 clinical scenarios where electrolytes can become deranged?
- 6 clinical scenarios where electrolytes can become deranged:
1) Haemorrhage - accidents, surgery
2) D&V
3) Poor intake - elderly
4) Increased losses - pyrexia, heat
5) Diuretic therapy
6) Endocrine disorders - Diabetes insipidus, Diabetes mellitus, disorders of ADH, aldosterone etc.
What are 3 compensatory mechanisms for deranged electrolytes?
What are 3 therapeutic interventions for deranged electrolytes?
- 3 compensatory mechanisms for deranged electrolytes:
1) Thirst
2) ADH (anti-diuretic hormone)
3) Renin / Angiotensin system - 3 therapeutic interventions for deranged electrolytes:
1) Intravenous therapy
2) Diuretics
3) Dialysis
In what state does the body fluid system normally exist in?
What can change in a factor cause?
- Normally the body fluid system is maintained in equilibrium
- Changing any factor causes a new steady state to be reached
In what clinical scenarios could be lose 2L of isotonic fluid?
How does this affect the body fluid system?
- We could lose 2L of isotonic fluid from blood or fistula fluid
- There is:
1) Loss is from ECF
2) No change in [Na]
3) No fluid redistribution
What happens if we replace the 2L loss of isotonic fluid with isotonic fluid or hypotonic fluid?
- If we replace the 2L loss of isotonic fluid with isotonic fluid:
1) No change in [Na]
2) No fluid redistribution - If we replace the 2L loss of isotonic fluid with isotonic fluid:
1) Fall in [Na]
2) Fluid redistribution
Where could we lose 3L of hypotonic fluid from?
How does this affect the body fluid system?
- We could lose 3L of hypotonic fluid from insensible loss
- Insensible fluid loss is the amount of body fluid lost daily that is not easily measured, from the respiratory system, skin, and water in the excreted stool
- This leads to:
1) Greater loss from ICF than ECF
2) Small increase in [Na]
3) Fluid redistribution between ECF & ICF
When is ADH release stimulated?
What 2 changes does ADH release leads to?
How do we measure ADH?
- ADH release is stimulated in response to a rise in concentration of osmotically active particles (increase in osmolality, particularly in sodium - It is actually osmolarity which is measured, but universally known and reported as osmolality)
- 2 changes ADH release leads to:
1) Decreased renal water loss
2) Increases thirst - ADH analysis is not readily available – assess status by:
1) Measuring plasma & urine osmolality
2) Urine > plasma suggests ADH is active
RAAS.
When is renin released?
In what 2 situations can IVV decrease?
What is the role of aldosterone?
How can we assess RAAS status?
- RAAS
- Renin release is activated by reduced intra-vascular volume (IVV)
- 2 situations IVV can decrease:
1) Na depletion
2) Haemorrhage - Aldosterone induces renal Na retention
- Simple test to ascertain RAAS status:
- Measure plasma & urine Na
- If urine < 10 mmol/L suggests R/A/A active
Why are urine reference intervals difficult to establish?
What should we be concerned with?
What is a rough concentration for urine (in picture):
* Sodium
* Potassium
* Urea
* Osmolality
* Creatinine
- Reference intervals for urine are difficult to establish as the kidney has an enormous capacity to save & excrete analytes as required – The concentration of the urine will affect the concentration of different substances it contains
- Therefore, we are most concerned with what is appropriate for the blood results and clinical situation e.g. if blood Na+ is normal, we wont be concerned about the Na+ urine concentration
What is urea is a breakdown product of?
Where is it filtered?
What volume enters the tubular lumen per day?
How much of this is urea?
- Urea is a normal breakdown product of protein
- It is filtered at the glomerulus & a major component of urine.
- ~200L plasma ultrafiltrate enters tubular lumen per day
- This represents typically 800 mmol (48g) of urea.
What is urea a sensitive marker of?
What does the concentration of urea often parallel?
What are 5 clinical scenarios where urea is elevated?
When can we see low urea levels?
- Urea is a sensitive marker of dehydration.
- Sodium & urea concentrations often parallel each other during fluid correction – so as we rehydrate, both concentrations come down
- 5 clinical scenarios where urea is elevated:
1) Gastric bleed
2) CCF
3) Shock
4) MI
5) Severe burns. - Low urea levels can be seen with low protein intake and patients with on IV fluids
What is creatinine a breakdown product of?
How is it filtered at the glomerulus?
What do plasma and urine values of creatinine reflect?
- Creatinine is a breakdown product of protein and muscle
- It is usually filtered freely at the glomerulus
- Plasma and urine values of creatinine typically reflect muscle mass – the more muscle mass, the higher the concentration of creatinine
How does renal function affect plasma concentrations of urea and creatinine?
What are urea and creatinine used as markers for?
When do we check for renal function?
- Loss of renal function leads to a decrease in filtered volume & hence an increase in plasma concentrations of urea & creatinine.
- Urea & creatinine used as markers of renal dysfunction.
- Checking renal function often necessary prior to starting certain drug treatments
What is GFR?
What can it be used as a measure of?
What 4 factors is GFR influenced by?
What is the normal range for GFR?
How does GFR vary with age and size of patient?
What does a decrease in GFR precede?
- GFR (glomerular filtration rate) is the volume of fluid passing through the glomerulus, in a given period of time
- GFR is the ultimate measure of kidney function
- 4 factors GFR is influenced by:
1) Renal perfusion pressure
2) Renal vascular resistance
3) Glomerular damage
4) Post-glomerular resistance - “Normal Range” is approximately 90 - 150 mL/min (Approx 170 L per day)
- Can be reported as 90 - 150 mL/min/1.73m2
- A larger healthy person has a higher GFR
- GFR values fall with increasing age.
- A decrease in GFR precedes renal failure in all forms of progressive kidney disease
How difficult is measuring GFR?
What can be used instead?
What is eGFR use for?
What formula can be used to calculate it?
What are AKI flags used for?
What do they highlight?
What are EGFR and AKI flags both calculated based on?
- Measuring GFR is difficult, so we can use eGFR (e =estimated)
- EGFR is used to aid “staging” of chronic kidney disease
- Various formulae for EGFR are available, some specific for e.g. cancer
- AKI flags are used to flag up incipient Acute Kidney Injury
- They highlight subtle changes in renal function.
- EGFR and AKI flags are both calculated based on creatinine
What are 3 causes of Low sodium?
What are 2 causes of High sodium?
What are 2 causes of dehydration?
- 3 causes of Low sodium:
1) Too little Na in ECF
2) Excess water in ECF
3) (Pseudo hyponatraemia due to ¬protein or lipid) - 2 causes of High sodium:
1) Too little water in ECF
2) Too much Na in ECF - 2 causes of dehydration:
1) Water deficiency
2) Fluid (Na & water) depletion
What are 3 steps in testing for Pseudohyponatraemia?
What are results of blood tests predicated on?
What can occur if this is not the case?
- 3 steps in testing for Pseudohyponatraemia:
1) Analytes such as Na are dissolved in the sample.
2) Fats & proteins are suspended in the sample
3) Suspended particles displace water. - Results of blood tests are predicated on the assumption that concentrations of fat, lipids and proteins are “normal”
- If this is not so, then results may have significant error
- Due to pseudohyponatremia, patients may have chronically low sodium, but the cause can’t be found
Describe the Low Sodium of unknown cause flowchart
Case 1: Dehydrated with difficulty swallowing
